The free electron laser represents an improvement in the field of high power coherent radiation sources. In this device a beam of relativistic electrons is caused to pass through a static periodic magnetic field with resultant amplification of a superimposed coherent optical input. The electrons in the beam are accelerated and decelerated and the laser action is thought to result from stimulated Compton backscattering of the virtual photons in the periodic magnet, or stimulated magnetic bremsstahlung. Unlike atomic lasers which provide a coherent light output at only a single frequency related to the energy levels of electrons in the atom, free electron lasers are continuously tunable within a range by varying the energy of the beam of electrons and/or by changes in the parameters of the periodic magnetic field. For more information regarding the operation and structure of such a free electron laser, reference may be made to U.S. Pat. No. 3,822,410. In prior art free electron lasers, the static periodic (wiggler) field varies in the axial direction of the drift tube used to provide an evacuated Faraday cage cavity for the electron beam. Difficulty has been experienced in achieving an ultrashort wavelength radiation output because of the relatively fast decay of the high multipole fields provided by the wiggler.
A gyrotron is a form of microwave generator based upon the cyclotron maser interaction betweeen an electromagnetic wave and a beam of relativistic electrons in which the individual electrons move along helical paths in the presence of the applied magnetic field. Cyclotron resonance coupling offers the advantage that both the electron beam and the microwave structures can have dimensions which are large compared to the output wavelength. One of the primary uses for a high power gyrotron is considered to be for fusion ignition in fusion research experimentation. For further information regarding the operation of a gyrotron, reference may be made to U.S. Pat. No. 3,398,376, "Electron Cyclotron Maser", Hirshfield and Wachtel, Physical Review Letters, Vol. 12, No. 19, May 1964, pages 533-536, and Hirchfield, J. L., et al., "The Electron Cyclotron Maser--An Historical Survey," IEEE Transactions on Microware Theory and Techniques, Vol. MTT-25, No. 6, June 1977, pp. 522-527.
There is a need for a coherent radiation source capable of providing an output in the infrared, visible and ultraviolet range. Potential uses include those of conventional atomic lasers such as communications, diagnostics, photochemistry (selective chemical reaction, isotope separation and very large scale integrated circuitry manufacture) and biomedical research.